Armor plate and process of making same



Patented May 29, 1923.

UNITED?JSTATE EY n ment Ann" rnoc'nss- OF MAKINGSAME NojDrawing.

To aZZ imam-ama comm i Be'it' known that we, Fn'ANoIs' BRADLEY; and HARRY L'. FnEvnR'n'citizens of the United States; residing at Philadelphia, "county of;

Philadelphia, and Staten-f Pennsylvania," have invented a newand useful Improve- 1 ment' in Armor Plates "and "Processes of Making Same, of which the following is a full, clear, and exact description, reference beinghad-to the accompanyin drawings, which form a part of this specification.

In an application filed by us June 27, 1922, Serial No. 571,301, we set forth the dis covery that if armorplate which is already treated, by known methods, to produce a plate having a hardened front with acarburized face, and a tough back, is drawn at a temperature above 500 F. and below 1100 F so as to remove from the hard front practically all the brittleness and a large portion of the hardness, while maintaining the stiffness required to offer extraordinary resistance vto displacement, it will offer greater resistance to penetration, with projectiles of the present improved type, than is offered by a plate of the ordinary type, wherein the hard front of the plate is unable to break the'point of the projectile and is itself cracked and spalled off with less expenditure of power than would be required were the metal to remain in pogreat resistance to displaceapplication for patentby still further in-.

creasing the resistance of the plate to perforation and at the same time prevent cracking under the shock of impact. g

A plate of the type to which our invention is applicable may be produced, for example, by the following process, well known to those skilled in the art: An ingotof any suitable composition is cast, and after reheating is forged or rolled into a late of a thickness about 20% in excess of t e thickness desired for the finished plate. The plate, thus formed, may be reheated and annealed, or reheated to below the critical temperature and cooled either quickly or slowly. The side of the plate intended for theface is then cleaned of all scale and .a brick container built around its edges. The container is filled with a suitablecarburizing compound, and a similar plate is laid face down upon it, the pair of plates being then heated Banners BRADLEY gam y. L; r mmin "maltr a ed;'paa 'symnms, 1

'to 'a' temperature and fora time suitabletfor penetration of carbon into the face" of the plate, to the desired depth and extent,v or j the platemay be carburizedby' a gas: I

, by the'ab-sorptionthereby of th'e desired car'- bon,- thei plate isf'carefully' cooled, and freed of scale, the face protected by a carbonaceous After the carburization of the plat'e,

covering, reheated to'a very low forging temperature I and forged .to,

low its critical temperature, bent and cooled Application fi1ed:.]iinfe 27-, 1922.- sria1Iva-571,302:

final thicknessp'a The plate is then reheated to a temperature" f considerably above its critical temperature, quenched, again reheated, but to a less de slowly; again reheated to a point well be- I low' its-critical temperature and quenched. The face of the plate is then heated rapidly to well above its critical'temperature, while the back is kept below that temperature-and the plate quenched throughout.

In this 1 heating operation, the temperature of the plate israisedjto above the critical temperature to .a depth substantially exceeding the relatively thin carburized face zone and "it is this part of the plate, which includes the carburized face and a zone to the rear thereof, which I call the front.

In the above described and other well known processes of face hardening armor 1 plateit is. present practice to harden to'a depth, in the case (say) of a 13% inch plate, of substantially less than five inches to not over about six inches or from thirty-five-to less than forty-five percent of the thickness of the plate.- Increase ofthe hardened zone, in the case of plates, of the present type, would not only not give greater re-V.

sistance to penetration, but would be detrimental, as it'would tionately thin tough back. In manufacturing our improved armor plate, however, we

find that if the plate (say 13%} inc-hes in thickness) is hardened to a depth varyingfrom substantially over six inches tonearly nine inches, or from at least forty-five per cent to about sixty-five percent of the thickness of the plate, and is then drawnat a temperature of from 500 to 1100 degrees F. (preferably 650. degrees F.), the resistance of the plate'toperforation will be still further increased, while, by reason of the removal of =1-10 J hardness'from theinitially hardened plate, f

at the back is suft the brittleness and av large portion of the the tough or ductile zone provide a disproporby Letters Patent? is:.., l

fieiently thick-to prevent cracking of; the plate under shock of impact.

The hardening of the plate to the depth specified is effected by the same methods, well known to those skilled in the art, generally used for hardening the plate to a. sub stantially less depth.

In producing the initially; hardened plate we first carburize the face to a depth of the thickness of the plate;v

This application is, a continuation in part of applicationSeriil' No. 505,883, filed 0.0-. tober 6,1921.

Hnvingnow tion, what we claim and desire to protect 1 The process; of so treetingermor plate as to; render It res stant to" perforation,

which comprises treating the plate to pro;-

(preferably) from seven to tenpercent of.

fully deseni bed our invem.

duce e tough back and a, carbnrized face hardened front. to adepth of from" fortyfive to sixty-five per cent of the thickness of t e pl te, a d n aw ng the p ate t a temperature not below 500 degrees F; nor above. 1100 degrees F.

2. As 21'- new article of manufacture, an armor plate provided with a toughba-ck end a. stiff carburized hardened front from which the normal brittleness has been substantially removed and whose normal hardness has n su stan lly d min sh d, the d p h o the de-brittled, stiff zone of reduced herds ness being from forty-five to sixty-five per cent of the thickness of the plate,

In testimony of which invention, we have on t 21 t day o i June; 1922- hereuntO Set our hands at Philada., Penna., I

FRANCIS BRADLEY;

HARRY L. FREVERJT. 

